Ideas to repair a dead 48V 10Ah Li-Ion Battery Pack?

[casainho]

I put the first 4 cells charging at limited current of 200mA and set the voltage to 16.4V, then I took this picture:

After I limited the current to 500mA and let the cells charge for 2 hours, tested and the battery is back again to life!!!
Then I left the cells charging for 7 hours, tested it and finally placed back on bicycle. I made long ride to discharge the battery a bit and put it again to charge. Now I am using a device to measure the power used by the charger and monitor it, since the green LED doesn't mean it is fully charged... (it needs time on the charge to balance the cells):


Many thanks to everyone that participated and helped!

Now I am back to focus on my project EBike Smart Controller (OpenSource).

 

[dnmun]

while you have it apart you may wanna test the capacity by discharging the pack into a dummy load. if you follow the voltages of each cell at the BMS while it is discharging you can see which is the one with the lowest capacity.

you have to make sure they are all fully charged to 4.2V first, and then discharge the pack into the load. i use oil filled radiators for the dummy load and discharge the pack through a wattmeter or my ammeter and follow the voltage down to cutoff.

i consider this to be the most valuable info to have about the pack. if something happens later, you can use the testing now to determine which cell has changed in capacity. also you can tell if there is really anything really wrong with the pack now if it doesn't produce the full 10Ah when you discharge it under controlled conditions like this kinda bench test.

 

[casainho]

while you have it apart you may wanna test the capacity by discharging the pack into a dummy load. if you follow the voltages of each cell at the BMS while it is discharging you can see which is the one with the lowest capacity.

you have to make sure they are all fully charged to 4.2V first, and then discharge the pack into the load. i use oil filled radiators for the dummy load and discharge the pack through a wattmeter or my ammeter and follow the voltage down to cutoff.

i consider this to be the most valuable info to have about the pack. if something happens later, you can use the testing now to determine which cell has changed in capacity. also you can tell if there is really anything really wrong with the pack now if it doesn't produce the full 10Ah when you discharge it under controlled conditions like this kinda bench test.

I do not have much time to do all that. I guess I will simple use the battery as I need it and I will "feel" if something is wrong or not due to lack of capacity to km traveled. Now I know that I need to keep it on the charge even after green LED, for it to balance and so I will have more available power for me to use

 

[999zip999]

Have you check for balance of the cells fully charged ? To see if one hasn't rest to high ?

 

[casainho]

Have you check for balance of the cells fully charged ? To see if one hasn't rest to high ?

No, I just discharged the battery a bit by riding the bicycle and put it on charge, I hope that BMS do it's work and ballance all the cells.

 

[dnmun]

this is a limn2o4 chemistry and it doesn't balance like the lifepo4 chemistry. with only 40mA of balancing current to drain the high cells. if the pack is unbalanced by 8Ah off between hi and lo, that means it will take 8/.04=200 hours for the high cells to drain off as much as the low cells need to fill up from the charger.

 

[casainho]

this is a limn2o4 chemistry and it doesn't balance like the lifepo4 chemistry. with only 40mA of balancing current to drain the high cells. if the pack is unbalanced by 8Ah off between hi and lo, that means it will take 8/.04=200 hours for the high cells to drain off as much as the low cells need to fill up from the charger.

I have time to wait for it balance, even if is 1 week or more. But I don't know and I would like to know, if the BMS balance only when battery is connected to charger??

 

[dnmun]

you have to have the charger connected in order to charge up the low cells.

 

[casainho]

you have to have the charger connected in order to charge up the low cells.

Ok, thanks.